2 Network Address Translation Overview Chapter 5 Network Address Translation Overview When a client attempts to access a server in a data center, the client incorporates its IP address in the IP header when it connects to the server. An ACE placed between the client and the server can either preserve the client IP address or translate that IP address to a routable address in the server network, based on a pool of reserved dynamic NAT addresses or a static NAT address mapping, and pass the request on to the server. This IP address translation process is called Network Address Translation (NAT) or source NAT (SNAT). The ACE tracks all SNAT mappings to ensure that response packets from the server are routed back to the client. If your application requires that the client IP address be preserved for statistical or accounting purposes, do not implement SNAT. Destination NAT (DNAT) translates the IP address and port of an inside host so that it appears with a publicly addressable destination IP address to the rest of the world. Typically, you configure DNAT using static NAT and port redirection. You can use port redirection to configure servers that host a service on a custom port (for example, servers hosting HTTP on port 8080). To provide security for a server, you can map the server private IP address to a global routable IP address that a client can use to connect to the server. In this case, the ACE translates the global IP address to the server private IP address when sending data from the client to the server. Conversely, when a server responds to a client, the ACE translates the local server IP address to a global IP address for security reasons. This process is called DNAT. You can also configure the ACE to translate TCP and UDP port numbers greater than 1024, and ICMP identifiers. This process is known as Port Address Translation (PAT). The ACE provides 64 K minus 1 K ports for each IP address for PAT. Ports 0 through 1024 are reserved and cannot be used for PAT. By default, the ACE performs implicit PAT for the FTP/RTSP/SIP data/media channel if you enable Layer 7 load-balancing or inspection. This identifies the real server from the server farm when the client sends data on the data/media channel using VIP and ACE performs real server IP to VIP translation for the data/media channel. (ACE module only) Implicit PAT is also performed for the same source/destination port and port redirection scenarios to ensure that the server response returns to the same network processor. 5-2

3 Chapter 5 Network Address Translation Overview (ACE module only) You can also disable implicit PAT and preserve the source port when the source and destination ports are the same by using the hw-module cde-same-port-hash in configuration mode. For details, see the Server Load-Balancing Guide, Cisco ACE Application Control Engine. The ACE supports the translation of IPv6 host or VIP addresses to IPv4 server addresses and the opposite for load balancing HTTP and HTTPS. This translation allow you to provide IPv6 functionality while maintaining an IPv4-only or an IPv6-only server farm or a server farm with a combination of the two protocols. Some of the benefits of NAT are as follows: You can use private addresses on your inside networks. Private addresses are not routable on the Internet. NAT hides the local addresses from other networks, so attackers cannot learn the real address of a server in the data center. You can resolve IP routing problems, such as overlapping addresses, when you have two interfaces connected to overlapping subnets. The ACE provides the following types of NAT and PAT: Interface-based dynamic NAT Interface-based dynamic PAT Server farm-based dynamic NAT Static NAT Static port redirection This section contains the following topics: Dynamic NAT Dynamic PAT Server Farm-Based Dynamic NAT Static NAT Static Port Redirection IPv6 NAT Support 5-3

4 Network Address Translation Overview Chapter 5 Maximum Number of NAT Commands Global Address Guidelines Dynamic NAT Dynamic NAT, which is typically used for SNAT, translates a group of local source addresses to a pool of global source addresses that are routable on the destination network. The global pool can include fewer addresses than the local group. When a local host accesses the destination network, the ACE assigns an IP address from the global pool to the host. Because the translation times out after being idle for a user-configurable period of time, a given user does not keep the same IP address. For this reason, users on the destination network cannot reliably initiate a connection to a host that uses dynamic NAT (even if the connection is allowed by an access control list [ACL]). Not only can you not predict the global IP address of the host, but the ACE does not create a translation unless the local host is the initiator. See the Configuring Static NAT and Static Port Redirection section for details about reliable access to hosts. For the duration of the translation, a global host can initiate a connection to the local host if an ACL allows it. Because the address is unpredictable, a connection to the host is unlikely. However, in this case, you can rely on the security of the ACL. Dynamic NAT has these disadvantages: If the global address pool has fewer addresses than the local group, you could run out of addresses if the amount of traffic is greater than expected. Use dynamic PAT if this event occurs often, because dynamic PAT provides over 64,000 translations using multiple ports of a single IP address. If you need to use a large number of routable addresses in the global pool and the destination network requires registered addresses (for example, the Internet), you may encounter a shortage of usable addresses. 5-4

5 Chapter 5 Network Address Translation Overview The ACE allows you to configure a virtual IP (VIP) address in the NAT pool for dynamic NAT and PAT. This action is useful when you want to source NAT real server originated connections (bound to the client) using the VIP address. This feature is specifically useful when there are a limited number of real world IP addresses on the client-side network. To perform PAT for different real servers that are source-nated to the same IP address (VIP), you must configure the pat keyword in the nat-pool command. The advantage of dynamic NAT is that some protocols cannot use dynamic PAT. Dynamic PAT does not work with some applications that have a data stream on one port and the control path on another, such as some multimedia applications. Dynamic PAT Dynamic PAT, which is also used for Source Network Address Translation (SNAT), translates multiple local source addresses and ports to a single global IP address and port that are routable on the destination network from a pool of IP addresses and ports reserved for this purpose. The ACE translates the local address and local port for multiple connections and/or hosts to a single global address and a unique port starting with port numbers greater than When a local host connects to the destination network on a given source port, the ACE assigns a global IP address to it and a unique port number. Each host receives the same IP address but, because the source port number is unique, the ACE sends the return traffic, which includes the IP address and port number as the destination, to the correct host. The ACE supports over 64,000 ports for each unique local IP address. Because the translation is specific to the local address and local port, each connection, which generates a new source port, requires a separate translation. For example, :1025 requires a separate translation from :1026. The translation is valid only for the duration of the connection, so a user does not keep the same global IP address and port number. For this reason, users on the destination network cannot reliably initiate a connection to a host that uses dynamic PAT (even if the connection is allowed by an ACL). Not only can you not predict the local or global port number of the host, but the ACE does not create a translation unless the local host is the initiator. See the Configuring Static NAT and Static Port Redirection section for details about reliable access to hosts. 5-5

6 Network Address Translation Overview Chapter 5 Dynamic PAT allows you to use a single global address, which helps to conserve routable addresses. Dynamic PAT does not work with some multimedia applications that have a data stream on a port that is different from the control path port. Server Farm-Based Dynamic NAT In addition to the interface-level dynamic NAT, the ACE supports dynamic NAT at the server farm level. Server farm-based dynamic NAT, which is also used for SNAT, is useful in situations where you want to perform NAT on only the IP addresses of the real servers in the primary and/or the backup server farm. Like interface-based dynamic NAT, server farm-based dynamic NAT uses a pool of IP addresses to translate a source address. Unlike interface-based NAT, server farm-based NAT translates the primary server farm IP addresses, the backup server farm IP addresses, or both. Use this feature in the following cases: The ACE is configured in one-arm mode, that is, there is only one VLAN between the ACE and the Cisco Systems 6500 and 7600 Series Catalyst MSFC that is used for both client and server traffic. Both the primary and backup server farms are in the internal customer network (reachable from the same VLAN or from different VLANs), the primary server farm is Layer 2-attached, and the backup server farm is several Layer 3 hops away. In this case, perform NAT only for the backup server farm and never for the primary server farm. The ACE is configured in one-arm mode, the primary server farm is local, and the backup server farm is remote and reachable from the public, external network. In this case, use a private pool of IP addresses for SNAT of the primary server farm and a public, externally routable set of IP addresses for the backup server farm. You want to perform source NAT based on a Layer 7 rule or the selected server farm. For details about configuring server farm-based dynamic NAT, see the Configuring Server Farm-Based Dynamic NAT section. 5-6

7 Chapter 5 Network Address Translation Overview Static NAT Static NAT, which is typically used for Destination NAT (DNAT), translates each local address to a fixed global address. With dynamic NAT and PAT, each host uses a different address or port after the translation times out. Because the global address is the same for each consecutive connection with static NAT, and a persistent translation rule exists, static NAT allows hosts on the global network to initiate traffic to a local host (if there is an ACL that allows it). The main differences between dynamic NAT and static NAT are as follows: Static NAT uses a one-to-one correspondence between a local IP address and a fixed global IP address, while dynamic NAT assigns a global IP address from a pool of global addresses. With static NAT, you need an equal number of global IP addresses and local IP addresses. With dynamic NAT, you can have a pool of fewer global addresses than local addresses. Static Port Redirection Static port redirection, also used for DNAT, performs the same function as static NAT and additionally translates TCP or UDP ports or ICMP identifiers for the local and global addresses. With static port redirection, you can use the same global address in multiple static NAT statements, provided that, along with the address, you use different port numbers. For example, if you want to provide a single address for global users to access FTP, HTTP, and SMTP, but there are different servers for each protocol on the local network, you can specify static port redirection statements for each server that use the same global IP address with different ports. IPv6 NAT Support As with IPv4 to IPv4 NAT, the ACE supports IPv6 to IPv6 NAT. The ACE also supports the translation of IPv6 or IPv4 VIPs in packets from clients to IPv4 or IPv6 server addresses for HTTP and HTTPS. This feature allows you to provide IPv6 functionality while maintaining an IPv4-only or an IPv6-only server farm infrastructure or a server farm with a combination of both protocols (mixed mode). 5-7

8 Network Address Translation Overview Chapter 5 This IPv6 implementation is useful for load balancing packets from an IPv6-only network to a an IPv4-only server farm or an IPv4-only network to an IPv6-only server farm. Be sure to configure the insertion of the X-Forwarded-For HTTP header field with the source address to ensure that the servers of one protocol can log the client addresses of the other protocol. For more information, see the Configuring NAT for IPv6 to IPv4 Load Balancing section and the Configuring NAT for IPv4 to IPv6 Load Balancing section. Maximum Number of NAT Commands The ACE supports the following maximum numbers of nat, nat-pool, and nat static commands divided among all contexts: nat command 8192 nat-pool command 8192 nat static command 8192 Global Address Guidelines When you translate the local address to a global address, you can use the following global addresses: Addresses on the same network as the global interface If you use addresses on the same network as the global interface (through which traffic exits the ACE), the ACE uses proxy ARP to answer any requests for translated addresses and thus intercepts traffic destined for a local address. This solution simplifies routing, because the ACE does not need to be the gateway for any additional networks. However, this approach does put a limit on the number of available addresses used for translations. You cannot use the IP address of the global interface for NAT or PAT. Addresses on a unique network If you need more addresses than are available on the global interface network, you can identify addresses on a different subnet. The ACE uses proxy ARP to answer any requests for translated addresses, so it intercepts traffic destined for a local address. You need to add a static route on the upstream router that sends traffic destined for the translated addresses on the ACE. 5-8

9 Chapter 5 Configuring an Idle Timeout for NAT You cannot configure global IP address ranges across subnets. For example, the following command is not allowed and will generate an Invalid IP address error: nat-pool netmask For IPv4, you must configure a netmask when you configure a NAT pool. A netmask of instructs the ACE to use all the IP addresses in the range. For IPv6, you must configure a prefix length when you configure a NAT pool. For example, /64. Configuring an Idle Timeout for NAT You can configure an idle timeout for NAT by using the timeout xlate command in configuration mode. The syntax of this command is as follows: timeout xlate seconds The seconds argument is an integer from 60 to The default is seconds (3 hours). The seconds value determines how long the ACE waits to free the Xlate slot after it becomes idle. For example, to specify an idle timeout of 120 seconds (2 minutes), enter: host1/admin(config)# timeout xlate 120 To reset the NAT idle timeout to the default value of seconds, enter: host1/admin(config)# no timeout xlate 120 Configuring Dynamic NAT and PAT This section describes how to configure dynamic NAT and PAT on an ACE for SNAT. For overview information about dynamic NAT and dynamic PAT, see the Network Address Translation Overview section. This section contains the following topics: Dynamic NAT and PAT Configuration Quick Start Configuring an ACL Configuring Interfaces for Dynamic NAT and PAT 5-9

10 Configuring Dynamic NAT and PAT Chapter 5 Creating a Global IP Address Pool for NAT Configuring a Class Map Configuring a Policy Map Configuring Dynamic NAT and PAT as a Layer 3 and Layer 4 Policy-Map Action Applying the Dynamic NAT and PAT Policy Map to an Interface Using a Service Policy Dynamic NAT and PAT Configuration Quick Start Table 5-1 provides a quick overview of the steps required to configure dynamic NAT and PAT. Each step includes the CLI command or a reference to the procedure required to complete the task. For a complete description of each feature and all the options associated with the CLI commands, see the sections following Table 5-1. Table 5-1 Dynamic NAT and PAT Configuration Quick Start Task and Command Example 1. If you are operating in multiple contexts, observe the CLI prompt to verify that you are operating in the desired context. If necessary, change to the correct context. host1/admin# changeto C1 host1/c1# The rest of the examples in this table use the C1 user context, unless otherwise specified. For details on creating contexts, see the Virtualization Guide, Cisco ACE Application Control Engine. 2. Enter configuration mode. host1/c1# config host1/c1(config)# 3. Configure an ACL to allow traffic that requires NAT. host1/c1(config)# access-list NAT_ACCESS extended permit tcp eq 80 host1/c1(config-acl)# exit 5-10

13 Chapter 5 Configuring Dynamic NAT and PAT host1/c1(config)# host1/admin(config)# access-list NAT_ACCESS line 10 extended permit tcp 2001:DB8:1::/ :DB8:2::/64 eq 80 To delete the ACL from the configuration, enter: host1/c1(config)# no access-list NAT_ACCESS IPv4 Syntax and Examples To configure an ACL for dynamic NAT, use the access-list command in configuration mode. The syntax of this command is as follows: access-list name [line number] extended {deny permit} {protocol} {src_ip_address netmask any host src_ip_address} [operator port1 [port2]] {dest_ip_address netmask any host dest_ip_address} [operator port3 [port4]] For example, enter: host1/c1(config)# access-list NAT_ACCESS extended permit tcp eq 80 To delete the ACL from the configuration, enter: host1/c1(config)# no access-list NAT_ACCESS Configuring Interfaces for Dynamic NAT and PAT Configure an interface for clients and an interface for the real servers. If you are operating the ACE in one-arm mode, do not configure an interface for clients. For details, see the Routing and Bridging Guide, Cisco ACE Application Control Engine. Creating a Global IP Address Pool for NAT Dynamic NAT uses a pool of global IP addresses that you specify. You can define either a single global IP address for a group of servers with PAT to differentiate between them, or a range of global IP addresses when using dynamic NAT only. To use a single IP address or a range of addresses, you assign an identifier to the address pool. You configure the NAT pool on the server VLAN interface. 5-13

14 Configuring Dynamic NAT and PAT Chapter 5 If a packet egresses an interface that you have not configured for NAT, the ACE transmits the packet untranslated. To create a pool of IP addresses for dynamic NAT, use the nat-pool command in interface configuration mode. IPv6 Syntax and Examples The syntax of this command is as follows: nat-pool pool_id {ipv6_address1[/prefix_length]} {ipv6_address1 ipv6_address2} [pat] The keywords, arguments, and options are as follows: pool_id Identifier of the NAT pool of global IP addresses. Enter an integer from 1 to If you configure more than one NAT pool with the same ID, the ACE uses the last-configured NAT pool first, and then the other NAT pools. ipv6_address1/prefix_length Single IPv6 address and optional prefix length, or if you are also using the ipv6_address2 argument, the first IPv6 address in a range of global addresses used for NAT. ipv6_address2 (Optional) Highest IPv6 address in a range of global IPv6 addresses used for NAT. You can configure a maximum of 64 K addresses in a NAT pool. If you specify PAT, you can configure a maximum of 32 IP addresses in a NAT pool range. You cannot configure an IP address range across subnets. For example, the following command is not allowed and will generate an Invalid IP address error: nat-pool :DB8:1::1 2001:DB8:2::

15 Chapter 5 Configuring Dynamic NAT and PAT The ACE allows you to configure a virtual IP (VIP) address in the NAT pool for dynamic NAT and PAT. This action is useful when you want to source NAT real server originated connections (bound to the client) using the VIP address. This feature is specifically useful when there are a limited number of real world IP addresses on the client-side network. To perform PAT for different real servers that are source-nated to the same IP address (VIP), you must configure the pat keyword in the nat-pool command. pat (Optional) Specifies that the ACE perform Port Address Translation (PAT) in addition to NAT. If the ACE runs out of IP addresses in a NAT pool, it can switch over to a PAT rule, if configured. For example, you can configure the following: host1/admin(config-if)# nat-pool :DB8:1::10/ :DB8:1::99/64 host1/admin(config-if)# nat-pool :DB8:1::100/ :DB8:1::100/64 pat If your network configuration has the following conditions, you should configure multiple PAT pools with a single IP address in each pool: Traffic coming from the same source IP address Source ports varying from 1 to The same destination port going to different destination addresses All ports in one PAT pool are used So instead of configuring: host1/admin(config-if)# nat-pool :DB8:1::3 2001:DB8:1::5 pat configure: host1/admin(config-if)# nat-pool :DB8:1::3/64 pat host1/admin(config-if)# nat-pool :DB8:1::4/64 pat host1/admin(config-if)# nat-pool :DB8:1::5/64 pat To configure a NAT pool consisting of a range of 32 (the maximum number of IP addresses per PAT pool) global IP addresses with PAT, enter: host1/c1(config)# interface vlan 200 host1/c1(config-if)# nat-pool :DB8:1::A/ :DB8:1::29/64 pat 5-15

16 Configuring Dynamic NAT and PAT Chapter 5 Before you can remove a NAT pool from an interface, you must remove the service policy and the policy map associated with the NAT pool. To remove a NAT pool from the configuration, enter: host1/c1(config-if)# no nat-pool 1 IPv4 Syntax and Examples The syntax of this command is as follows: nat-pool pool_id ip_address1 [ip_address2] netmask mask [pat] The keywords, arguments, and options are as follows: pool_id Identifier of the NAT pool of global IP addresses. Enter an integer from 1 to If you configure more than one NAT pool with the same ID, the ACE uses the last-configured NAT pool first, and then the other NAT pools. ip_address1 Single IP address, or if also using the ip_address2 argument, the first IP address in a range of global addresses used for NAT. Enter an IP address in dotted-decimal notation (for example, ). ip_address2 (Optional) Highest IP address in a range of global IP addresses used for NAT. Enter an IP address in dotted-decimal notation (for example, ). You can configure a maximum of 64 K addresses in a NAT pool. If you specify PAT, you can configure a maximum of 32 IP addresses in a NAT pool range. You cannot configure an IP address range across subnets. For example, the following command is not allowed and will generate an Invalid IP address error: nat-pool netmask

17 Chapter 5 Configuring Dynamic NAT and PAT The ACE allows you to configure a virtual IP (VIP) address in the NAT pool for dynamic NAT and PAT. This action is useful when you want to source NAT real server originated connections (bound to the client) using the VIP address. This feature is specifically useful when there are a limited number of real world IP addresses on the client-side network. To perform PAT for different real servers that are source-nated to the same IP address (VIP), you must configure the pat keyword in the nat-pool command. netmask mask Specifies the subnet mask for the IP address pool. Enter a mask in dotted-decimal notation (for example, ). A network mask of instructs the ACE to use all the IP addresses in the specified range. pat (Optional) Specifies that the ACE perform Port Address Translation (PAT) in addition to NAT. If the ACE runs out of IP addresses in a NAT pool, it can switch over to a PAT rule, if configured. For example, you can configure the following: host1/admin(config-if)# nat-pool netmask host1/admin(config-if)# nat-pool netmask pat If your network configuration has the following conditions, you should configure multiple PAT pools with a single IP address in each pool: Traffic coming from the same source IP address Source ports varying from 1 to The same destination port going to different destination addresses All ports in one PAT pool are used So instead of configuring: host1/admin(config-if)# nat-pool netmask pat configure: host1/admin(config-if)# nat-pool netmask pat 5-17

18 Configuring Dynamic NAT and PAT Chapter 5 host1/admin(config-if)# nat-pool netmask pat host1/admin(config-if)# nat-pool netmask pat To configure a NAT pool consisting of a range of 32 (the maximum number of IP addresses per PAT pool) global IP addresses with PAT, enter: host1/c1(config)# interface vlan 200 host1/c1(config-if)# nat-pool netmask pat Before you can remove a NAT pool from an interface, you must remove the service policy and the policy map associated with the NAT pool. To remove a NAT pool from the configuration, enter: host1/c1(config-if)# no nat-pool 1 Configuring a Class Map You can configure a traffic class for dynamic NAT and PAT by using the class-map command in configuration mode. For more information about class maps, see the Administration Guide, Cisco ACE Application Control Engine. The syntax of this command is as follows: class-map match-any name The name argument is a unique identifier for the class map, specified as an unquoted text string with a maximum of 64 alphanumeric characters. For example, enter: host1/c1(config)# class-map match-any NAT_CLASS host1/c1(config-cmap)# To remove a class-map from the configuration, enter: host1/c1(config)# no class-map match-any NAT_CLASS 5-18

19 Chapter 5 Configuring Dynamic NAT and PAT Enter match criteria for the ACL or the client source address using the match command in class-map configuration mode. For example, to set the match criteria to an existing ACL, enter the following command: host1/c1(config-cmap)# match access-list NAT_ACCESS or For IPv6, enter: host1/c1(config-cmap)# match source-address 2001:DB8:1::10/64 For IPv4, enter: host1/c1(config-cmap)# match source-address To remove a match statement from a class map, enter: host1/c1(config-cmap)# no match access-list NAT_ACCESS Configuring a Class Map for Passive FTP If you are using passive FTP with source NAT, you must configure an additional class map to source NAT the passive data connection. You then associate this class map with the Layer 4 multimatch policy and configure the nat dynamic command as an action in the policy map under this class map. To configure a class map for passive FTP, enter the commands in the following examples. For IPv6, enter: host1/c1(config)# class-map match-any FTP_NAT_CLASS host1/c1(config-cmap)# match virtual address 2001:DB8:1::10 any For Ipv4, enter: host1/c1(config)# class-map match-any FTP_NAT_CLASS host1/c1(config-cmap)# match virtual address any Configuring a Policy Map You can configure a traffic policy for dynamic NAT and PAT by using the policy-map command in configuration mode. For more information about policy maps, see the Administration Guide, Cisco ACE Application Control Engine. 5-19

20 Configuring Dynamic NAT and PAT Chapter 5 The syntax of this command is as follows: policy-map multi-match name The name argument is the name assigned to the policy map. Enter an unquoted text string with no spaces and a maximum of 64 alphanumeric characters. For example, enter: host1/c1(config)# policy-map multi-match NAT_POLICY host1/c1(config-pmap)# To remove a policy map from the configuration, enter: host1/c1(config)# no policy-map multi-match NAT_POLICY Associate the previously created class map with the policy map. For example, enter: host1/c1(config-pmap)# class NAT_CLASS host1/c1(config-pmap-c)# To dissociate a class map from a policy map, enter: host1/c1(config-pmap)# no class NAT_CLASS Configure policy-map actions as required. For example, configure: host1/c1(config-pmap-c)# loadbalance policy L7_POLICY host1/c1(config-pmap-c)# loadbalance vip inservice The loadbalance vip inservice command is not valid with a match access-list or a match source-address class map. For passive FTP, associate the FTP_NAT_CLASS class map (see the Configuring a Class Map for Passive FTP section) with the Layer 4 policy map. For example, enter the following commands in policy map configuration mode: host1/c1(config)# policy-map multi-match NAT_POLICY host1/c1(config-pmap)# class FTP_NAT_CLASS If you are using passive FTP, proceed with the following section and configure the nat dynamic command as a policy action under the FTP class map. Otherwise, configure the nat dynamic command as a policy action under the NAT_CLASS class map. 5-20

21 Chapter 5 Configuring Dynamic NAT and PAT Configuring Dynamic NAT and PAT as a Layer 3 and Layer 4 Policy-Map Action You can configure dynamic NAT and PAT (SNAT) as an action in a Layer 3 and Layer 4 policy map by using the nat dynamic command in policy-map class configuration mode. The ACE applies dynamic NAT from the interface to which the traffic policy is attached (through the service-policy interface configuration command) to the interface specified in the nat command. If you are operating in one-arm mode, there is only one VLAN interface. The syntax of this command is as follows: nat dynamic pool_id vlan number The keywords, arguments, and options are as follows: dynamic pool_id Refers to the identifier of a global pool of IP addresses that was configured using the nat-pool command on the specified VLAN (see the Creating a Global IP Address Pool for NAT section). Dynamic NAT translates a group of local source IP addresses to a pool of global IP addresses that are routable on the destination network. All packets egressing the interface attached to the traffic policy have their source address translated to one of the available addresses in the global pool. Enter an integer from 1 to vlan number Specifies the server interface for the global IP address. This interface must be different from the interface that the ACE uses to filter and receive traffic that requires NAT, unless the network design operates in one-arm mode. In that case, the VLAN number is the same. If a packet egresses an interface that you have not configured for NAT, the ACE transmits the packet untranslated. The following example specifies the nat command as an action for a dynamic NAT Layer 3 and Layer 4 policy map: host1/c1(config)# policy-map multi-action NAT_POLICY host1/c1(config-pmap)# class NAT_CLASS host1/c1(config-pmap-c)# nat dynamic 1 vlan 200 To remove a dynamic NAT action from a policy map, enter: 5-21

22 Configuring Dynamic NAT and PAT Chapter 5 host1/c1(config-pmap-c)# no nat dynamic 1 vlan 200 Applying the Dynamic NAT and PAT Policy Map to an Interface Using a Service Policy Activate the dynamic NAT and PAT policy map and associate it with an interface by using the service-policy command in interface configuration mode. For details about the service-policy command, see the Administration Guide, Cisco ACE Application Control Engine. You can configure dynamic NAT as an input service policy only, not as an output service policy. You cannot apply the same NAT policy both locally and globally. The syntax of this command is as follows: service-policy input policy_name The keywords and arguments are as follows: input Specifies that the traffic policy is to be attached to the input direction of a VLAN interface. The traffic policy evaluates all traffic received by that interface. policy_name Name of a previously defined policy map. The name can have a maximum of 64 alphanumeric characters. IPv6 Example To apply a service policy to a specific interface for IPv6, enter: host1/c1(config)# interface vlan 100 host1/c1(config-if)# mtu 1700 host1/c1(config-if)# ip address 2001:DB8:1::2/64 host1/c1(config-if)# service-policy input NAT_POLICY To apply a service policy globally to all interfaces in a context, enter: host1/c1(config)# service-policy input NAT_POLICY To remove a service policy from an interface, enter: host1/c1(config-if)# no service-policy input NAT_POLICY 5-22

23 Chapter 5 Configuring NAT for IPv6 to IPv4 Load Balancing To remove a service policy globally from all interfaces in a context, enter: host1/c1(config)# no service-policy input NAT_POLICY IPv4 Example To apply a service policy to a specific interface for IPv6, enter: host1/c1(config)# interface vlan 100 host1/c1(config-if)# mtu 1700 host1/c1(config-if)# ip address host1/c1(config-if)# service-policy input NAT_POLICY To apply a service policy globally to all interfaces in a context, enter: host1/c1(config)# service-policy input NAT_POLICY To remove a service policy from an interface, enter: host1/c1(config-if)# no service-policy input NAT_POLICY To remove a service policy globally from all interfaces in a context, enter: host1/c1(config)# no service-policy input NAT_POLICY When you detach a traffic policy either individually from the last VLAN interface on which you applied the service policy or globally from all VLAN interfaces in the same context, the ACE automatically resets the associated service-policy statistics. The ACE performs this action to provide a new starting point for the service-policy statistics the next time that you attach a traffic policy to a specific VLAN interface or globally to all VLAN interfaces in the same context. Configuring NAT for IPv6 to IPv4 Load Balancing You can configure the ACE to act as a proxy and translate VIP addresses in packets from clients in an IPv6 network to IPv4 real server addresses. This configuration allows you to implement IPv6 in your network while maintaining your current IPv4 real servers. When a client sends an IPv6 packet to an ACE IPv6 VIP, the ACE translates the VIP address to a server IPv4 private address and sends the packet to the server. In the absence of a specific configuration, the IPv6 address of the client would be lost and the IPv4 server would not be able to log the client IPv6 address. To ensure that the IPv4 server can log the client IPv6 5-23

25 Chapter 5 Configuring NAT for IPv4 to IPv6 Load Balancing nat dynamic 1 vlan 3001 interface vlan 2001 ipv6 enable ip address 2001:DB8:1::2002/96 access-group input all access-group input v6-any service-policy input V6_Policy1 service-policy input MGMT no shutdown interface vlan 3001 ip address nat-pool netmask pat no shutdown Configuring NAT for IPv4 to IPv6 Load Balancing You can configure the ACE to act as a proxy and translate VIP addresses in packets from clients in an IPv4 network to IPv6 real server addresses. This configuration allows you to implement IPv6 in your network and connect to IPv4 networks. When a client sends an IPv4 packet to an ACE IPv4 VIP, the ACE translates the VIP address to a server IPv6 unique local address and sends the packet to the server. In the absence of a specific configuration, the IPv4 address of the client would be lost and the IPv6 server would not be able to log the client address. To ensure that the IPv6 server can log the client IPv4 address, you must configure the X-Forwarded-For: HTTP header on the ACE. For example, the following configuration shows how to implement NAT for IPv4 to IPv6 load balancing. The NAT-specific commands are shown in bold. access-list all line 8 extended permit ip any any access-list v6-any line 8 extended permit ip anyv6 anyv6 rserver host v6_rs1 ip address 2001:DB6:1::10 inservice rserver host v6_rs2 ip address 2001:DB6:1::11 inservice serverfarm host v6_sf1 rserver v6_rs1 inservice 5-25

32 Configuring Server Farm-Based Dynamic NAT Chapter 5 Configuring an ACL for Server Farm-Based Dynamic NAT Use an access control list (ACL) to permit the traffic that requires NAT. See the Configuring an ACL section. For details about configuring an ACL, see Chapter 1, Configuring Security Access Control Lists. Configuring Interfaces for Server Farm-Based Dynamic NAT Configure an interface for clients and an interface for the real servers. If you are operating the ACE in one-arm mode, omit the client interface. For details about configuring interfaces, see the Routing and Bridging Guide, Cisco ACE Application Control Engine. Creating a Global IP Address Pool for Dynamic NAT Dynamic NAT uses a pool of global IP addresses that you specify. You can define a range of global IP addresses when using dynamic NAT. To use a range of addresses, you assign an identifier to the address pool. You then associate the NAT pool with the server VLAN interface. If a packet egresses an interface that you have not configured for NAT, the ACE transmits the packet untranslated. To create a pool of IPv6 addresses for dynamic NAT, use the nat-pool command in interface configuration mode. If you plan to apply both IPv6 and IPv4 addresses under the same NAT pool because your configuration includes a mixed mode server farm (a mixture of IPv6 and IPv4 servers), also refer to the Configuring a Mixed Mode (IPv6 and IPv4) Server Farm section for additional configuration information. 5-32

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